Apparatus for dehydrogenation of liquid hydrides

ABSTRACT

An apparatus for the dehydrogenation of liquid hydrides consisting of a chemical reactor (18) to dehydrogenate the heated vaporous hydrides, a pre-heating stage (12a, 12b) to pre-heat the hydride, a vaporization stage (14a, 14b), to vaporize the hydride, a superheating stage (16a, 16b) to superheat the vaporous hydrides and a condensation stage (10a, 10b) to cool the dehydrogenation products. All stages, including the reactor, are designed as plate-shaped hybrid heat exchangers stacked side by side. Two cylindrical storage containers (6a, 6b) for the dehydrogenation products are located at both front ends of the heat exchanger stack. Side plates (30, 32) linked to the storage containers (6a, 6b) function as tie rods, providing the apparatus, in conjunction with the storage containers with the required stability. The spaces (36, 38) between the side plates and the heat exchanger stack hold guide channels for the flow media. In particular, the apparatus is distinguished by its inexpensive design, compactness and low weight.

This is a continuation of application Ser. No. 07/350,750, filed May 3,1989 and now abandoned.

The invention involves an apparatus for the dehydrogenation of liquidhydrides with a chemical reactor, designed as a heat exchanger, for thedehydrogenation of heated vaporous hydride, a heat exchanger fluid toheat the hydride, at least one combustion chamber to heat the heatexchanger fluid by burning hydrogen, at least one heat exchanger to heatthe hydride fed to the reactor using the heat exchanger fluid or thedehydrogenation products leaving the reactor, at least one heatexchanger to cool down the dehydrogenation products leaving the reactorand at least one storage container for the cooled dehydrogenationproducts leaving the reactor.

In particular, the invention refers to an apparatus for thedehydrogenation of liquid hydrides suitable to drive hydrogen-poweredvehicles.

A fundamental problem in the development of practical vehicles driven bymeans of hydrogen-powered combustion engines is how to store thehydrogen suitably in the vehicles. In this regard, it has proven usefulfrom various points of view to make use of the organic-chemical storageof hydrogen in liquid hydrides. Methyl cyclohexane, which is a liquidthat can be stored in simple tanks under normal pressure and at a normaltemperature, is especially suited as a liquid hydride. The hydrogen isstored by dehydrogenation of toluene to methyl cyclohexane.

Methyl cyclohexane is pumped into the vehicle as a liquid hydridecarrier. The vehicle contains a dehydrogenation system in which themethyl cyclohexane (MCH) is split into toluene and hydrogen in achemical reactor using the application of heat and a suitable catalyst.The hydrogen recovered in this way is stored temporarily and used mainlyto drive the hydrogen-powered combustion engine, but in part also togenerate the heat in the reactor required for dehydrogenation. Theliquid toluene produced during dehydrogenation is also stored andreturned to the pump the next time the vehicle is filled up. The toluenecan then be dehydrogenated once again to MCH in suitable dehydrogenationplants, closing the cycle.

Appropriate test set-ups were developed which showed that the aforesaidprocess can definitely be realized in practice. However, in the case ofthese test set-ups the dehydrogenation system including the necessaryauxiliary equipment and measuring equipment, was of such a volume thatit took up the space of the loading area of a truck or of a trailer.This is one of the basic reasons why this technology is not yetrealizable in practice at present.

The objective of the invention, therefore, is to create an apparatus forthe dehydrogenation of liquid hydrides of the type mentioned at thebeginning. These hydrides are especially distinguished by the fact thatthey are compact, lightweight and inexpensive to produce.

As claimed, this objective is essentially solved by the fact that thechemical reactor and the heat exchangers are all plate-shaped, that theplate-shaped heat exchangers are stacked side by side, that a storagecontainer is placed on each front end of the heat exchanger stack andthe two storage containers enclose the heat exchanger stack betweenthem, that plates acting as tie rods are place on both sides of thestack (these plates being attached to opposite end sections of thestorage containers and at a distance from the heat exchanger stack) andthat at least one combustion chamber as well as baffle and connectingchannels, via which the various heat exchangers are linked together, areplaced in the space between the side plates and the opposite sides ofthe heat exchanger stack.

The plate-shape region of the heat exchangers and their stack-shapedarrangement creates an extremely space-saving configuration. As thereaction medium is under a pressure of 10 to 20 bar, the apparatus mustbe very stable. This high stability is attained through the especiallysimple structural method of placing the heat exchanger packet betweenthe storage containers located at the ends, which can be made ofsufficiently strong material, and through the side plates, whichfunction as tie rods and which are linked to the storage containers,absorbing the forces acting on the storage containers in a simple way.Therefore, it is possible to make the plate-shaped heat exchangers, inwhich an operating pressure of approximately 20 bar prevails, of thinmaterial while reducing costs and material expenditures, since thepressure forces are absorbed by the clamp-shaped storage container/sideplate arrangement surrounding the heat exchanger packet.

A particularly space and material-saving arrangement also results fromthe fact that the combustion chamber used to heat the heat exchangerfluid by burning hydrogen as well as the baffle or rather connectingchannels linking the various heat exchangers together are placed in thespace between the side plates and the opposite sides to them of the heatexchanger stack. In addition, this also results in the various fluidshaving to travel especially short distances, which also contributes tothe apparatus being highly efficient.

In the ideal design of the invention, the storage containers arepartially cylindrical, the cylinder axis running parallel to theplate-shaped heat exchangers, the diameter of the partial cylinder beinggreater than the width of the heat exchanger stack and the partialcylinder extending more than 180° in the radial direction. Accordingly,the partially cylindrical storage containers extend beyond the heatexchanger stack on both sides, the side plates of the apparatus beinglocated almost tangentially to the partially cylindrical walls of thestorage containers and welded to them at this point. The partiallycylindrical shape of the storage containers gives them high mechanicalstability with, at the same time, comparatively thin wall strengths. Inan appropriate subsequent development of the invention, it is planned toarrange the heat exchangers in a such away that the chemical rector islocated in the middle of the heat exchanger stack and that the less hotheat exchangers are connected to it in an outward direction. If severalheat exchangers are used, the mean temperature, in particular, of theindividual heat exchangers may decrease from the interior towards theexterior. This keeps heat losses low and also reduces insulationproblems.

In accordance with an especially ideal feature of the invention, theapparatus is designed symmetrically in such a way that identical heatexchanger stages are attached to both sides of the rector located in themiddle. Consequently, all of the other heat exchanger stages, with theexception of the reactor, are provided twice in an identical fashion andthe process runs twice in both directions in an identical fashionbetween the central reactor and the two storage containers on the sides.More specifically, a heat exchanger serving as a superheating stage canbe placed on each side of the reactor, then on both sides of these heatexchangers serving as a vaporization stage, then on both sides of theseheat exchangers serving as a pre-heating stage and on both sides ofthese heat exchangers serving as a cooling stage or condenser. Thefluids circulate in such away that the hydride passes through thepre-heating stages, the vaporization stages, the superheating stages andthe reactor one after the other, in such away that, after thedehydrogenation of the hydride, the dehydrogenation products (H₂ andtoluene and nonreactive MCH) pass through the superheating stages, thepreheating stages and the cooling stages and in such away that the heatexchanger fluid used to heat the hydride in the rector and in thevaporization stages--where it is used with H₂ combustion engines, theengine exhaust air--passes through the vaporization stages after passingthrough the reactor.

In accordance with an especially ideal feature of the invention, anextremely compact, very highly efficient apparatus results if theplate-shaped heat exchangers are designed as a hybrid heat exchanger ofa type which is basically known, consisting in each case of a number ofstamped profiled sheets which are welded together and which definebetween them alternately a large number of parallel tube-shaped flowmedium channels and a number of slot-shaped, wave-like channels verticalto the former. Such hybrid heat exchangers combine the resistance toheat and pressure of a tube exchanger with the compact andmaterial-saving design of a plate exchanger, heating surfaces densitiesof up to 250 m² exchange surface per cubic meter of structural volumebeing realizable. The wave-shaped course of the transverse flow channelsproduces great turbulences and, thus, excellent heat transmissionconditions. For example, suitable hybrid heat exchangers are offered byIPG Bavaria, Industrieplanungsgesellschaft mbH fur thermischeVerfahrenstechnik /Industrial Planning Private Limited Company forThermal Process Engineering/, Munich, under the name IPEX-Hybrid.

Further advantageous features of the invention result from the othersub-claims and from the description below in which an ideal example ofthe invention is described in more detail using the drawing. The drawingcontains:

FIG. 1 a diagrammatic representation of the dehydrogenation process ofthe claimed apparatus,

FIG. 2 a side view of the claimed apparatus in a half-diagrammaticrepresentation.

FIG. 3 a top view of the claimed apparatus in a half-diagrammaticrepresentation.

FIG. 4 a sectional view of the individual heat exchanger stages of theapparatus in accordance with FIG. 2 viewed in the direction of arrow IV,the individual heat exchanger stages being shown side by side in alateral view with only half of the apparatus being illustrated, and

FIG. 5 a section through a hybrid heat exchanger of the claimedapparatus.

Reference is first made to the basic diagram in FIG. 1. It should benoted that, in contrast to the illustrations in FIGS. 2 and 3, a singleheat exchanger stage is illustrated in the basic diagram in FIG. 1,whereas in the case of the example shown in FIGS. 2 to 4 two identicalheat exchanger stages are provided. However in the interests of claritythe second set of heat exchanger stages was not illustrated in FIG. 1.

In FIG. 1, reference number 2 designates a dehydrogenation apparatusused to dehydrogenate the liquid hydride, specifically methylcyclohexane (MCH), stored in a vehicle tank 4. MCH, which represents anorganic carrier of hydrogen, is fed from the tank 4 of thedehydrogenation apparatus 2 under a pressure of approximately 20 barinto the dehydrogenation apparatus 2 where it is split catalytically andwith the application of heat into hydrogen and toluene. The hydrogenrecovered through this process is stored temporarily in a storagecontainer 6 and used to power the hydrogen engine 8 driving the vehicle,for example a truck. The hot exhaust air of the hydrogen engine 8 is fedto the dehydrogenation apparatus 2 in order to heat the reactor. Sincethe heat transferred from the engine exhaust gases to thedehydrogenation apparatus 2 is not sufficient to meet the heartrequirements of the dehydrogenation unit, the heat deficit in thedehydrogenation apparatus is covered by burning part of the hydrogenproduced.

The cycles illustrated in FIG. 1 are discussed in more detail below.

The dehydrogenation apparatus 2 is made up of a condensation stage 10, apre-heating stage 12, a vaporization stage 14, a superheating stage 16and a chemical reactor 18. The MCH in the tank 4 is fed to thedehydrogenation apparatus 2 via the pump 20 under a pressure ofapproximately 20 bar, where it first passes through the pre-heatingstage 12 designed as heat exchangers in which it is pre-heated to atemperature of approximately 235° C. Then the pre-heated MCH passesthrough the vaporization stage 14, which is also designated as heatexchangers, in which the MCH, which has been liquid up to this point, isheated further and vaporized. The MCH vapor is then passed through thesuperheating stage 16 designed as heat exchangers in which the vapor issuperheated to approximately 390° C., just under the reactiontemperature. The superheated vapor then enters the reactor 18 in whichit is dehydrogenated catalytically with the application of further heat,hydrogen and vaporous toluene being produced as the main dehydrogenationproducts.

The hydrogen-toluene mixture exhausted from the reactor 18 now has atemperature of approximately 420° C. and is once again fed into thesuperheating stage 16 where it transfers part of its heat to the MCH tobe superheated. After leaving the superheating stage 16, thehydrogen-toluene mixture has a temperature of approximately 250° C. andis then fed to the pre-heating stage 12 in which it pre-heats the liquidMCH coming from the tank 4. Finally, the hydrogen-toluene mixture whichhas been cooled down passes through the condensation stage 10 in whichthe toluene is further cooled and condensed. Air is provided as thecooling medium for the condensation stage 10 in the example describedhere. This air is fed to the heat exchanger 10 via a fan 22. Obviously,cooling water, for example, could also be used as an alternative coolingmedium.

The dehydrogenation products cooled to approximately 30° C.,specifically hydrogen and toluene in the main, are finally stored orstored temporarily in storage container 6, the toluene being in liquidform, the hydrogen in vaporous form. In addition, if desired, thetoluene can be separated from the hydrogen in a manner not described inmore detail.

In order to heat the reactor 18, hot exhaust air from the hydrogenengine is fed top it. Because, as already mentioned, the temperature ofthe exhaust air from the hydrogen engine is not sufficient to meet theheat requirement of the reactor 18, additional hydrogen is burned insuitable combustion chamber 24, 26 and 28 of the reactor 18 in order toraise the temperature of the exhaust air from the hydrogen engine toapproximately 650° C. In order to assure a uniform distribution of theheat over the entire reactor, the latter is designed in three stages intotal. Each stage has a combustion chamber 24, 26 or 28 respectively inwhich the exhaust air which has been cooled down to approximately 420°C. is heated again to 650° C.

After passing through the reactor 18, the exhaust air from the hydrogenengine flows through the vaporizer 14 in which it is cooled down toapproximately 330° C. while transferring heat to the MCH. Then theexhaust air is exitted into the atmosphere.

Reference is made below to FIGS. 2 to 5.

As can be sen from FIGS. 2 and 3, the dehydrogenation apparatus 2consists of one unified block. It is made upon of the centrally locatedreactor 18 and, attached to each side of it, a superheating stage 16a,16b, a vaporization stage 14a, 14b, a preheating stage 12a, 12b, acondensation stage 10a, 10b and a storage container 6a, 6b. Each of thestages 10a. 10b, 12a, 12b, 14a, 14b, 16a and 16b as well as the reactor18 are designed as plate-shaped heat exchangers and have in thedirection of arrow IV in FIG. 2 essentially the same dimensions. Theindividual plate-shaped heat exchangers are stacked side by side so thatthey form a unified block, as can be seen clearly from FIGS. 2 and 3. Astorage container 6a, 6b is placed at both ends of the heat exchangerblock. Each storage container is partially cylindrical and its axisextends parallel to the longitudinal side of the individual heatexchanger plates. The diameter of the partially cylindrical storagecontainers 6a, 6b is, as can be clearly seen in FIG. 3, greater than thedepth of the heat exchanger packet so that the storage containers 6a, 6bproject laterally beyond the heat exchanger packet. Side plates 30, 32are provided which run parallel to the lateral surfaces of the heatexchanger packet and which are welded firmly to the storage containerson both edges facing the storage containers 6a, 6b in such a way thatthe side plates 30, 32 run almost tangentially to the partiallycylindrical storage containers 6a, 6b. As can be seen in FIG. 2, thehead pieces allocated to the individual heat exchangers close the heatexchangers at the top. A lower closing plate 34 is weeded to the storagecontainers 6a, 6b by its front end and to the side plates 30, 32 alongits longitudinal side, closing the heat exchanger packet at the bottom.

As is explained below in more detail, the individual heat exchangers 10ato 16b and the reactor 18 consist of individual, comparatively thinplates which are not capable of containing the high operating pressureprevailing in the heat exchanger packet without additionalreinforcement. In the case of the claimed arrangement, the pressure isabsorbed by the two storage containers 6a, 6b at the ends. These storagecontainers are made of sufficiently strong material and, in any case,exhibit a high inherent stability based on their cylindricalconfiguration. The side plates 30, 32 lining the two storage containers6a, 6b serve as tie rods between the two storage containers 6a, 6b, sothat the heat exchanger packet is bracketed by the two side plates and,as a result, the pressure occurring are absorbed by the dehydrogenationapparatus in the simplest way.

The guide and baffle channels for the fluids flowing through theindividual heat exchangers and the combustions chambers 24 to 28 arelocated in the spaces 36 and 38 between the side plates 30, 32 and theopposite side walls of the heat exchanger packet.

The individual heat exchangers 10a to 16b each consist of hybrid heatexchangers as illustrated in cross-section in FIG. 5. Each heatexchanger consists of several plate elements 40 welded together whichexhibit stampings of such a kind that a weeded plate packet hastube-like flow medium channels in the one direction--in the case of thesectional view in FIG. 5, vertical to the drawing plane--and slot-shapedflow medium channels extending wave-like from one side to the other ofthe plate packet in a transverse direction--in the case of theillustration in FIG. 5, horizontally. The tube-like flow medium channels42 are called tubes below, the slot-shaped, wave-like flow mediumchannels slots.

Reference will be made below to the illustration in FIG. 4. Only half ofthe arrangement illustrated in FIGS. 2 and 3 is illustrated in FIG. 4.However the other half is completely identical so that explanation ofthe one half is sufficient to understand the invention.

The MCH fed from the tank 4 (compare FIG. 1) to the dehydrogenationapparatus 2 enters the pre-heating stage 12 from below and passesthrough the vertical running slots of the heat exchanger. The heatexchanger of the pre-heating stage 12 consists of six compartments 12.1,12.2, 12.3, 12.4, 12.5 and 12.6 stacked on top of one another whoseslots are linked together. The tubes are arranged horizontally and thedehydrogenation products coming from the superheating steps 16 flowthrough each compartment one after the other, starting with the uppercompartment 12.6 and ending the lower compartment 12.1. As illustratedby the arrows, the dehydrogenation products mainly flow serpentine-likein the pre-heating stage 12 from the top to the bottom, so that the twocomponents flow through the pre-heating stage 12 on a counter-currentbasis. Suitable guide plates are placed* in the lateral spaces 36, 38 inorder to bring about the serpentine-like flow through the individualcompartments 12.1 to 12.6.

The pre-heated MCH leaves the pre-heating stage 12 at its upper side andis then fed to the upper side of the vaporization stage 14. The slots ofthe heat exchanger also run vertically and the tubes transversely tothem, horizontally, in this vaporization stage. The MCH first flowsthrough the vaporization stage 14 from the top to the bottom and then onthe opposite side of the heat exchanger from the bottom to the top. Thestampings in the middle of the plate elements ensure that the leftsection of the heat exchanger is separated from the right in FIG. 4.

The heated exhaust air coming from the reactor 18 flows from above viathe space 38 into the vaporization stage 14 and reaches, after flowingthrough the tubes of the heat exchanger, the space 36, from which itexits into the atmosphere.

The now vaporous MCH leaving the vaporization stage 14 is fed to thesuperheating stage 16 from above and leaves it from the lower end. Thedeign of the superheating stage 16 corresponds to that of thepre-heating stage 12; in particular, the superheating stage 16 is alsocomposed of six compartments 16.1 to 16.6 which are stacked on top ofone another and which the dehydrogenation products leaving the reactor18 flow through from the top to the bottom, meander-like. The twocomponents flow through the superheating stage 16 on a counter-currentbase as well.

The various MCH exitting at the bottom of the superheating stage 16 isthen fed from the top to the reactor 18 in which the slots of the heatexchanger once again run vertically, so that the MCH passes through thereactor wave-like from the top to the bottom. The reactor 18 isconstructed of three stages 18.1, 18.2 and 18.3 stacked on top of oneanother, the exhaust air form the hydrogen engine passing through eachstage 18.1 to 18.3 one after the other. By means of baffle plates in thespaces 36, 38, the exhaust air is directed through successive stages inalternately opposing direction. The baffle plates 46, 48 in the spaces36, 38 define chambers 24, 26, 28 into which hydrogen feed pipes 50, 52,54 open, in each case into the lower section. Additional hydrogen isburned in these combustion chambers 24, 26 and 28 in order, as describedabove, to heat the exhaust air from the hydrogen engine to the requiredreaction temperature.

As is clear from FIG. 4, on the whole the reactor 18 is also operated oncounter-current basis.

The dehydrogenation products leaving the lower end of the pre-heatingstage 12, specifically hydrogen and toluene in the main, are fed to theupper side of the condensation stage 10 whose heat exchanger hasvertical continuous slots and horizontal tubes. In order to cool downthe hydrogen-toluene mixture, fresh air is fed to the tubes of the heatexchanger 10 from below via space 38 by means of a fan. This fresh airpasses through the heat exchanger from right to left, is collected inspace 36 and exitted upwards into the atmosphere.

Finally, the cooled hydrogen-toluene mixture is exitted to the bottom ofthe condensation stage 10 and then fed to the storage container, inwhich the hydrogen is stored temporarily for further use.

    ______________________________________    REFERENCE NUMBER LIST    ______________________________________     2            Dehydrogenation apparatus     4            Tank     6            Storage container     8            Hydrogen engine    10            Condensation stage    12            Pre-heating stage    14            Vaporization stage    16            Superheating stage    18            Reactor    20            Pump    22            Fan    24            Combustion chamber    26            Combustion chamber    28            Combustion chamber    30            Side plate    32            Side plate    34            Closing plate    36            Space    38            Space    40            Plate element    42            Tubes    44            Slots    46            Baffle plate    48            Baffle plate    ______________________________________

I claim:
 1. An apparatus for the dehydrogenation of liquid hydrides,comprisinga chemical reactor for the dehydrogenation of heated vaporoushydride wherein hydride fed to the reactor is heated by coolingdehydrogenation products leaving the reactor and further heated in thereactor by the heat of combustion hydrogen in a hot hydrogen-containinggas stream fed to the reactor and the cooled dehydrogenation productsare then stored in storage containers, and said chemical reactorcomprises a plurality of combustion chambers connected in series inwhich hydrogen is combusted and a reactor heat exchanger fortransferring heat from combusting hydrogen to dehydrogenating hydride,said reactor heat exchanger comprising a plurality of stages throughwhich the hydride passes during hydrogenation; said chemical rector isconnected in series with a superheating heat exchanger, a vaporizingheat exchanger and a preheating heat exchanger wherein said hydride tobe dehydrogenated passes through the preheating heat exchanger,vaporizing heat exchanger and superheating heat exchanger, in series,for heating, and said hydrogen liberated from said hydride in saidchemical reactor passes in the reverse direction from said chemicalreactor through the superheater heat exchanger and the preheating heatexchanger, for cooling; said reactor heat exchanger, superheating heatexchanger, vaporizing heat exchanger and preheating heat exchanger eachcomprise plate-type heat exchangers; said plate-type heat exchangers arestacked adjacent to each other in series; said storage containers forstoring the dehydrogenation products are positioned at each end of theheat exchanger stack having the heat exchanger stack therebetween; apair of substantially parallel plates acting as tie rods connect thestorage containers, one on each side of the heat exchanger stack; and achannel connecting said heat exchangers is placed in a space defined byeach of said pair of plates and sides of the heat exchanger stackopposite said plates.
 2. The apparatus in accordance with claim 1wherein said storage containers comprise a substantially cylindricalportion having a cylindrical axis running parallel to the length of saidplate-type heat exchangers and a diameter greater than the width of theheat exchanger stack and the cylindrical portion extends over more than180°.
 3. The apparatus in accordance with claim 1 wherein said chemicalrector is positioned in series with a superheating heat exchanger, avaporizing heat exchanger and a preheating heat exchanger on each sidethereof.
 4. The apparatus in accordance with claim 3 wherein said heatexchangers are attached to each side of the centrally positionedchemical reactor to form a symmetrical array of heat exchangers, and thetemperature of the individual heat exchangers decreases from the centerof the heat exchanger stack to the ends thereof.
 5. The apparatus inaccordance with claim 4 wherein condensers serving as a cooling stagefor the dehydrogenation products exiting the preheating heat exchangersare attached to each of the preheating heat exchangers.
 6. The apparatusin accordance with claim 1 wherein at least the reactor heat exchangers,the superheating heat exchangers and the preheating heat exchangers areconnected so that the inflowing fluid and the outflowing fluid flowcounter-currently within said heat exchangers.
 7. The apparatus inaccordance with claim 1 wherein the plate-type heat-exchangers arehybrid heat exchangers each comprising a plurality of wave-like shapedplates welded together and which define between them alternately aplurality of parallel, tube-shaped channels and a plurality ofslot-shaped wave-like channels perpendicular to said tube-shapedchannels.
 8. The apparatus in accordance with claim 1 adapted foroperation at a pressure of about 20 bar.